The long-term goal of the proposed research is to determine the function and basis of action of a class of T-lymphocytes that proliferate in response to autologous or syngeneic antigen presenting cells alone in the absence of foreign peptides, a response known as the autologous mixed lymphocyte reaction (AMLR). The AMLR is often deficient in patients with autoimmune diseases, and in several autoimmune strains of mice. However, direct evidence that a deficiency in AMLR contributes to the etiology of autoimmune diseases is lacking. Using the non-obese diabetic (NOD) mouse, an established animal model of the autoimmune disease insulin-dependent diabetes mellitus (IDDM), which manifests a characteristic deficiency in AMLR, we have generated seven T cell clones that proliferated vigorously to autologous spleen cells in the absence of foreign antigens. We have characterized their cellular properties in detail. We have demonstrated that two of the autoreactive clones (NOD-4 and NOD-5) were very effective in protecting NOD mice from insulitis and diabetes, while a FCS-specific NOD T cell clone was not. Furthermore, we have shown that the NOD-5 T cell clone exerted a profound inhibitory effect on allogeneic-MLR, a test often used to assess T-- suppressor function. The responses of the autoreactive T cell clones were CD4-dependent. However, a higher than usual amount of anti-CD4 mAb is required for inhibition of their responses. Immunoprecipitation with p56-lck antisera and in vitro kinase assay revealed a unique association of an 85 kD phosphoprotein (p85) with p56-lck in the autoreactive but not in the antigen-specific T cell clones. Such association has not. been previously reported for any T cells. We hypothesize that the autoreactive T cell clones may have a unique signal transduction mechanism via the CD4 molecule, which may potentiate weak TCR-peptide-MHC signals, and this may be the basis for the autoreactive responses. Based on these preliminary data, we have proposed to determine 1) the molecular basis of autoreactivity for the I-region specific autoreactive T cell clones that we have generated; 2) to determine the identity of p85, and the reason for its association with lck only in autoreactive T cell clones; and 3) to determine the molecular basis of the suppressive action of NOD-4 and NOD-5 against insulitis and diabetes in NOD mice, by examining the cellular mechanism of action of NOD-5 in suppressing allogeneic-MLR, and by further characterizing the in vivo actions of the autoreactive T cell clones. Our proposed experiments directed at systematic analysis of molecular mechanism of action at cell and molecular levels, should provide us with definitive informations regarding the basis of autoreactivity and their roles in the regulation of development of autoimmune diseases such as IDDM.